Method and apparatus for programmable fluidic processing

ABSTRACT

A method and apparatus for microfluidic processing by programmably manipulating a packet. A material is introduced onto a reaction surface and compartmentalized to form a packet. A position of the packet is sensed with a position sensor. A programmable manipulation force is applied to the packet at the position. The programmable manipulation force is adjustable according to packet position by a controller. The packet is programmably moved according to the programmable manipulation force along arbitrarily chosen paths.

This application is a continuation of co-pending U.S. application Ser.No. 14/452,047, filed Aug. 5, 2014, which is a continuation of U.S.application Ser. No. 13/545,775 filed Jul. 10, 2012 (and now issued asU.S. Pat. No. 8,834,810), which is a continuation of U.S. applicationSer. No. 12/622,775 filed Nov. 20, 2009 (and now issued as U.S. Pat. No.8,216,513), which is a continuation of U.S. application Ser. No.11/135,615 filed May 23, 2005 (and now issued as U.S. Pat. No.7,641,779), which is a continuation of U.S. application Ser. No.09/902,933 filed Jul. 10, 2001 (and now issued as U.S. Pat. No.6,977,033), which is a continuation of U.S. application Ser. No.09/249,955, filed Feb. 12, 1999 (and now issued as U.S. Pat. No.6,294,063). The entire text of each of the above-referenced disclosuresis specifically incorporated by reference herein without disclaimer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to fluidic processing and, moreparticularly, to a method and apparatus for programmably manipulatingand interacting one or more compartmentalized packets of material on areaction surface.

2. Description of Related Art

Chemical protocols often involve a number of processing steps includingmetering, mixing, transporting, division, and other manipulation offluids. For example, fluids are often prepared in test tubes, meteredout using pipettes, transported into different test tubes, and mixedwith other fluids to promote one or more reactions. During suchprocedures, reagents, intermediates, and/or final reaction products maybe monitored, measured, or sensed in analytical apparatus. Microfluidicprocessing generally involves such processing and monitoring usingminute quantities of fluid. Microfluidic processing finds applicationsin vast fields of study and industry including, for instance, diagnosticmedicine, environmental testing, agriculture, chemical and biologicalwarfare detection, space medicine, molecular biology, chemistry,biochemistry, food science, clinical studies, and pharmaceuticalpursuits.

A current approach to fluidic and microfluidic processing utilizes anumber of microfluidic channels that are configured with microvalves,pumps, connectors, mixers, and detectors. While devices usingmicro-scale implementations of these traditional approaches may exhibitat least a degree of utility, vast room for improvement remains. Forinstance, pumps and valves used in traditional fluidic transportationare mechanical. Mechanical devices, particularly when coupled to thinmicrochannels, may be prone to failure or blockage. In particular, thinchannels may become narrowed or partially-blocked due to buildup ofchannel contamination, which, in turn, may lead to mechanical failure ofassociated devices. Current microfluidic devices also lack flexibility,for they rely upon a fixed pathway of microchannels. With fixedpathways, devices are limited in the number and type of tasks they mayperform. Also, using fixed pathways makes many types of metering,transport, and manipulation difficult. With traditional devices, it isdifficult to partition one type of sample from another within a channel.

Electrical properties of materials have been employed to perform alimited number of fluidic processing tasks. For example,dielectrophoresis has been utilized to aid in the characterization andseparation of particles, including biological cells. An example of sucha device is described in U.S. Pat. No. 5,344,535 to Betts, incorporatedherein by reference. Betts establishes dielectrophoretic collectionrates and collection rate spectra for dielectrically polarizableparticles in a suspension. Particle concentrations at a certain locationdownstream of an electrode structure are measured using a light sourceand a light detector, which measures the increased or decreasedabsorption or scattering of the light which, in turn, indicates anincrease or decrease in the concentration of particles suspended in thefluid. Although useful for determining particle dielectrophoreticproperties, such a system is limited in application. In particular, sucha system does not allow for general fluidic processing involving variousinteractions, sometimes performed simultaneously, such as metering,mixing, fusing, transporting, division, and general manipulation ofmultiple reagents and reaction products.

Another example of using certain electrical properties for specifictypes of processing is disclosed in U.S. Pat. No. 5,632,957 to Heller etal., incorporated herein by reference. There, controlled hybridizationmay be achieved using a matrix or array of electronically addressablemicrolocations in conjunction with a permeation layer, an attachmentregion and a reservoir. An activated microlocation attracts chargedbinding entities towards an electrode. When the binding entity contactsthe attachment layer, which is situated upon the permeation layer, thefunctionalized specific binding entity becomes covalently attached tothe attachment layer. Although useful for specific tasks such as DNAhybridization, room for improvement remains. In particular, such asystem, utilizing attachment sites for certain binding entities isdesigned for particular applications and not for general fluidicprocessing of a variety of fluids. More specifically, such a system isdesigned for use with charged binding entities that interact withattachment sites.

Another example of processing is disclosed in U.S. Pat. No. 5,126,022 toSoane et al., incorporated herein by reference. There, charged moleculesmay be moved through a medium that fills a trench in response toelectric fields generated by electrodes. Although useful for tasks suchas separation, room for improvement remains in that such devices are notwell suited for performing a wide variety of fluidic processinginteractions on a wide variety of different materials.

There are other examples of using dielectrophoresis for performingspecific, limited fluidic processing tasks. U.S. Pat. No. 5,795,457 toPethig and Burt, incorporated herein by reference, disclose a method forpromoting reactions between particles suspended in liquid by applyingtwo or more electrical fields of different frequencies to electrodearrays. While perhaps useful for facilitating certain interactionsbetween many particles of different types, the method is not well suitedfor general fluidic processing. U.S. Pat. No. 4,390,403 to Batchelder,incorporated herein by reference, discloses a method and apparatus formanipulation of chemical species by dielectrophoretic forces. Althoughuseful for inducing certain chemical reactions, its flexibility islimited, and it does not allow for general, programmable fluidicprocessing.

Any problems or shortcomings enumerated in the foregoing are notintended to be exhaustive but rather are among many that tend to impairthe effectiveness of previously known processing techniques. Othernoteworthy problems may also exist; however, those presented aboveshould be sufficient to demonstrated that apparatus and methodsappearing in the art have not been altogether satisfactory.

SUMMARY OF THE INVENTION

In one respect, the invention is an apparatus for programmablymanipulating a packet. As used herein, “packet” refers tocompartmentalized matter and may refer to a fluid packet, anencapsulated packet, and/or a solid packet. A fluid packet refers to oneor more packets of liquids or gases. A fluid packet may refer to adroplet or bubble of a liquid or gas. A fluid packet may refer to adroplet of water, a droplet of reagent, a droplet of solvent, a dropletof solution, a droplet of sample, a particle or cell suspension, adroplet of an intermediate product, a droplet of a final reactionproduct, or a droplet of any material. An example of a fluid packet is adroplet of aqueous solution suspended in oil. An encapsulated packetrefers to a packet enclosed by a layer of material. An encapsulatedpacket may refer to vesicle or other microcapsule of liquid or gas thatmay contain a reagent, a sample, a particle, a cell, an intermediateproduct, a final reaction product, or any material. The surface of anencapsulated packet may be coated with a reagent, a sample, a particleor cell, an intermediate product, a final reaction product, or anymaterial. An example of an encapsulated packet is a lipid vesiclecontaining an aqueous solution of reagent suspended in water. A solidpacket refers to a solid material that may contain, or be covered with areagent, a sample, a particle or cell, an intermediate product, a finalreaction product, or any material. An example of a solid packet is alatex microsphere with reagent bound to its surface suspended in anaqueous solution. Methods for producing packets as defined herein areknown in the art. Packets may be made to vary greatly in size and shape,but in embodiments described herein, packets may have a diameter betweenabout 100 nm and about 1 cm.

In this respect, the invention includes a reaction surface, an inletport, means for generating a programmable manipulation force upon thepacket, a position sensor, and a controller. The reaction surface isconfigured to provide an interaction site for the packet. The inlet portis coupled to the reaction surface and is configured to introduce thepacket onto the reaction surface. The means for generating aprogrammable manipulation force upon the packet programmably moves thepacket about the reaction surface along arbitrarily chosen paths. Asused herein, by “arbitrarily chosen paths” it is meant that paths may bechosen to have any shape about the reaction surface. Arbitrarily chosenpaths are not limited to movements that are predefined. Arbitrarilychosen paths may be modified in an unlimited manner about the reactionsurface and may hence trace out any pattern. The position sensor iscoupled to the reaction surface and is configured to sense a position ofthe packet on the reaction surface. The controller is coupled to themeans for generating a programmable manipulation force and to theposition sensor. The controller is configured to adjust the programmablemanipulation force according to the position.

In other aspects, the apparatus may also include an outlet port coupledto the reaction surface. The outlet port may be configured to collectthe packet from the reaction surface. The means for generating amanipulation force may include a conductor adapted to generate anelectric field. The means for generating a manipulation force mayinclude a light source. The manipulation force may include adielectrophoretic force, an electrophoretic force, an optical force, amechanical force, or any combination thereof. The position sensor mayinclude a conductor configured to measure an electrical impedance of thepacket. The position sensor may include an optical system configured tomonitor the position of the packet. The means for generating aprogrammable manipulation force and the position sensor may be integral.

In another respect, the invention is an apparatus for microfluidicprocessing by programmably manipulating packets. The apparatus includesa reaction surface, an inlet port, an array of driving electrodes, andan array of impedance sensing electrodes. As used herein, an “array”refers to any grouping or arrangement. An array may be a lineararrangement of elements. It may also be a two dimensional groupinghaving columns and rows. Columns and rows need not be uniformly spacedor orthogonal. An array may also be any three dimensional arrangement.The reaction surface is configured to provide an interaction site forthe packets. The inlet port is coupled to the reaction surface and isconfigured to introduce the packets onto the reaction surface. The arrayof driving electrodes is coupled to the reaction surface and isconfigured to generate a programmable manipulation force upon thepackets to direct the microfluidic processing by moving the packetsalong arbitrarily chosen paths. The array of impedance sensingelectrodes is coupled to the reaction surface and is configured to sensepositions of the packets during the microfluidic processing.

In other aspects, the apparatus may also include an outlet port coupledto the reaction surface. The outlet port may be configured to collectthe packets from the reaction surface. The apparatus may also include acontroller coupled to the array of driving electrodes and to the arrayof impedance sensing electrodes. The controller may be adapted toprovide a feedback from the array of impedance sensing electrodes to thearray of driving electrodes. The array of driving electrodes and thearray of impedance sensing electrodes may be integral. The apparatus mayalso include an integrated circuit coupled to the array of drivingelectrodes and to the array of impedance sensing electrodes. Theapparatus may also include a coating modifying a hydrophobicity of thereaction surface. The apparatus may also include a maintenance port.

In another respect, the invention is an apparatus for processing packetsin a partitioning medium. As used herein, a “partitioning medium” refersto matter that may be adapted to suspend and compartmentalize othermatter to form packets on a reaction surface. A partitioning medium mayact by utilizing differences in hydrophobicity between a fluid and apacket. For instance, hydrocarbon molecules may serve as a partitioningmedium for packets of aqueous solution because molecules of an aqueoussolution introduced into a suspending hydrocarbon fluid will stronglytend to stay associated with one another. This phenomenon is referred toas a hydrophobic effect, and it allows for compartmentalization and easytransport of packets upon or over a surface. A partitioning medium mayalso be a dielectric carrier liquid which is immiscible with samplesolutions. Other suitable partitioning mediums include, but are notlimited to, air, aqueous solutions, organic solvents, oils, andhydrocarbons. The apparatus includes a chamber, a programmabledielectrophoretic array, and an impedance sensing array. As used herein,a “programmable dielectrophoretic array” (PDA) refers to an electrodearray whose individual elements can be addressed with differentelectrical signals. The addressing of electrode elements with electricalsignals may initiate different field distributions and generatedielectrophoretic manipulation forces that trap, repel, transport, orperform other manipulations upon packets on and above the electrodeplane. By programmably addressing electrode elements within the arraywith electrical signals, electric field distributions and manipulationforces acting upon packets may be programmable so that packets may bemanipulated along arbitrarily chosen or predetermined paths. The chamberis configured to contain the packets and the partitioning medium. Theprogrammable dielectrophoretic array is coupled to the chamber and isconfigured to generate a programmable dielectrophoretic force to directprocessing of the packets. The impedance sensing array of electrodes isintegral with the programmable dielectrophoretic array. The impedancesensing array of electrodes is configured to sense a position of thepackets within the chamber.

In other aspects, the apparatus may also include an integrated circuitcoupled to the programmable dielectrophoretic array and to the impedancesensing array of electrodes. The apparatus may also include a controllercoupled to the programmable dielectrophoretic array and to the impedancesensing array of electrodes. The controller may be adapted to provide afeedback from the impedance sensing array of electrodes to theprogrammable dielectrophoretic array. The electrodes may be betweenabout 1 micron and about 200 microns and may be spaced between about 1micron and about 200 microns.

In another respect, the invention is a method for manipulating a packetin which the following are provided: a reaction surface, an inlet portcoupled to the reaction surface, means for generating a programmablemanipulation force upon the packet, a position sensor coupled to thereaction surface, and a controller coupled to the means for generating aprogrammable manipulation force and to the position sensor. A materialis introduced onto the reaction surface with the inlet port. Thematerial is compartmentalized to form the packet. A position of thepacket is sensed with the position sensor. A programmable manipulationforce is applied on the packet at the position with the means forgenerating a programmable manipulation force. The programmablemanipulation force is adjustable according to the position by thecontroller. The packet is programmably moved according to theprogrammable manipulation force along arbitrarily chosen paths.

In other aspects, the packet may include a fluid packet, an encapsulatedpacket, or a solid packet. The compartmentalizing may include suspendingthe material in a partitioning medium. The material may be immiscible inthe partitioning medium. The reaction surface may include a coating, andthe hydrophobicity of the coating may be greater than a hydrophobicityof the partitioning medium. The application of the programmablemanipulation force may include applying a driving signal to one or moredriving electrodes arranged in an array to generate the programmablemanipulation force. The programmable manipulation force may include adielectrophoretic force, an electrophoretic force, an optical force, amechanical force, or any combination thereof. The sensing of a positionmay include applying a sensing signal to one or more impedance sensingelectrodes arranged in an array to detect an impedance associated withthe packet.

In another respect, the invention is a method of fluidic processing inwhich the following are provided: a reaction surface, an inlet portcoupled to the reaction surface, an array of driving electrodes coupledto the reaction surface, and an array of impedance sensing electrodescoupled to the reaction surface. One or more materials are introducedonto the reaction surface with the inlet port. The one or more materialsare compartmentalized to form a plurality of packets. A sensing signalis applied to one or more of the impedance sensing electrodes todetermine a position of one or more of the plurality of packets. Adriving signal is applied to one or more of the driving electrodes togenerate a programmable manipulation force on one or more of theplurality of packets at the position. One or more of the plurality ofpackets are interacted according to the programmable manipulation force.

In other aspects, at least one of the plurality of packets may include afluid packet, an encapsulated packet, or a solid packet. The sensingsignal and the driving signal may be a single processing signal. Theprocessing signal may include a first frequency component correspondingto the sensing signal and a second frequency component corresponding tothe driving signal. A packet distribution map may be formed according tothe positions of the plurality of packets. A position of one or moreobstructions on the reaction surface may be determined. The interactingof one or more packets may include moving, fusing, merging, mixing,reacting, metering, dividing, splitting, sensing, collecting, or anycombination thereof.

In another respect, the invention is a method for manipulating one ormore packets on a reaction surface in which the following are provided:a programmable dielectrophoretic array coupled to the reaction surfaceand an impedance sensing array of electrodes integral with theprogrammable dielectrophoretic array. A material is introduced onto thereaction surface. The material is compartmentalized to form the one ormore packets. A path is specified upon the reaction surface. Aprogrammable manipulation force is applied with the programmabledielectrophoretic array on the one or more packets to move the one ormore packets along the path. A position of the one or more packets issensed with the impedance sensing array of electrodes. Whether theposition corresponds to the path is monitored. The one or more packetsare interacted.

In other aspects, at lease one of the one or more packets may include afluid packet, an encapsulated packet, or a solid packet. The method mayalso include sensing a position of an obstruction; determining amodified path, the modified path avoiding the obstruction; and applyinga programmable manipulation force on the one or more packets to move theone or more packets along the modified path. The specification of a pathmay include specifying an initial position and a final position. Theintroduction of the material may include extracting the material with adielectrophoretic extraction force from an injector onto the reactionsurface. The interacting of one or more packets may include moving,fusing, merging, mixing, reacting, metering, dividing, splitting,sensing, collecting, or any combination thereof.

Other features and advantages of the present invention will becomeapparent with reference to the following description of typicalembodiments in connection with the accompanying drawings wherein likereference numerals have been applied to like elements, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram that illustrates a microfluidicdevice according to one embodiment of the presently disclosed method andapparatus.

FIG. 2 is a simplified illustration of dielectrophoretic forcephenomenon.

FIG. 3 illustrates a position sensing system according to one embodimentof the presently disclosed method and apparatus.

FIG. 4 is a three dimensional view of a microfluidic device according toone embodiment of the presently disclosed method and apparatus.

FIG. 5 is a side cross sectional view of a microfluidic device accordingto one embodiment of the presently disclosed method and apparatus.

FIG. 6 is a simplified block representation of a microfluidic systemaccording to one embodiment of the presently disclosed method andapparatus.

FIG. 7 is a simplified block representation of a signal applicationarrangement according to one embodiment of the presently disclosedmethod and apparatus.

FIG. 8 is a cross sectional view of microfluidic device according to oneembodiment of the presently disclosed method and apparatus.

FIG. 9 is a top view of a microfluidic device according to oneembodiment of the presently disclosed method and apparatus.

FIG. 9B is another top view of a microfluidic device according to oneembodiment of the presently disclosed method and apparatus.

FIG. 10 is a simplified block representation of a microfluidic systemaccording to one embodiment of the presently disclosed method andapparatus.

FIG. 11 is a top view of a microfluidic device showing a microfluidicprocess according to one embodiment of the presently disclosed methodand apparatus.

FIG. 12 illustrates certain packet interactions according to oneembodiment of the presently disclosed method and apparatus.

FIG. 13 is a flow chart showing a microfluidic process according to oneembodiment of the presently disclosed method and apparatus.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The disclosed method and apparatus provide many advantages. Forinstance, they permit the fluidic processing of minute quantities ofsamples and reagents. The apparatus need not use conventional hardwarecomponents such as valves, mixers, pump. The apparatus may be readilyminiaturized and its processes may be automated or programmed. Theapparatus may be used for many different types of microfluidicprocessing and protocols, and it may be operated in parallel modewhereby multiple fluidic processing tasks and reactions are performedsimultaneously within a single chamber. Because it need not rely onnarrow tubes or channels, blockages may be minimized or eliminated.Further, if obstructions do exist, those obstructions may be located andavoided with position sensing techniques.

Allowing for flexible microfluidic processing, the disclosed method andapparatus has vast applications including, but not limited to, blood andurine assays, pathogen detection, pollution monitoring, watermonitoring, fertilizer analysis, the detection of chemical andbiological warfare agents, food pathogen detection, quality control andblending, massively parallel molecular biological protocols, geneticengineering, oncogene detection, and pharmaceutical development andtesting.

In one embodiment of the disclosed method and apparatus, a fluidicdevice 10 as shown in FIG. 1 is employed. As illustrated, fluidic device10 may include a reaction surface 12, a port 15, packets 21, wall 22,position sensor 23, a force generator 25, and a controller 81.

In operation, one or more materials may be introduced onto reactionsurface 12 through port 15. The one or more materials may becompartmentalized to form packets 21 within a partitioning medium (notshown). Force generator 25 generates a manipulation force on packets 21to facilitate fluidic manipulations and interactions. In the illustratedembodiment, force generator 25 generates two forces, F₁ and F₂, thatmanipulate packets 21 and moves them according to the dashed lines ofFIG. 1. Position sensor 23 senses the positions of packets 21 and isable to monitor any packet interactions. As position sensor 23 iscoupled to force generator 25 by controller 81, a feedback relationshipmay be established. Such feedback may include determination of theposition of packets 21 on reaction surface 12 that allows for theapplication of manipulation forces on packets 21 based on positioninformation. The position of packets during manipulation may thus becontinuously monitored and this information may be used to continuouslyadjust one or more manipulation forces so to achieve movement of packets21 along a desired trajectory to a desired location on reaction surface12.

In the illustrated embodiment of FIG. 1, forces F₁ or F₂ may includemany different types of forces. For instance, forces F₁ and F₂ may bedielectrophoretic, electrophoretic, optical (as may arise, for example,through the use of optical tweezers), mechanical (as may arise, forexample, from elastic traveling waves or from acoustic waves), or anyother suitable type of force (or combination thereof). In oneembodiment, forces F₁ and F₂ may be programmable. Using programmableforces, packets may be manipulated along arbitrarily chosen paths.

In the illustrated embodiment of FIG. 1, position sensor 23 may beoperated with various mechanisms to sense positions of packets 21. Forinstance, an optical imaging system may be used to determine and monitorpacket positions. Specifically, an optical microscope may be connectedto a CCD imaging camera, which may be interfaced with an imaging card ina computer. The information from the imaging card may be processed inthe computer using image-analysis software. Alternatively, a CCD imagingdevice may be incorporated in or above the reaction surface 12 tomonitor the positions of packets. Thus, positions of packets and theirmovement on reaction surface 12 may be continuously monitored andrecorded in the computer. A different mechanism of packet positionsensing uses electrical impedance measurements. The presence or absenceof a packet between two electrode elements may affect the electricalimpedance between the electrodes. Thus, measurement of electricalimpedance between electrode elements may allow for indirect monitoringof packet positions.

In order to better understand the operation and design of the currentlydisclosed method and apparatus, which will be discussed first inrelation to dielectrophoretic forces, it is useful to discussdielectrophoretic theory in some detail. Such a discussion is aided byFIG. 2, which illustrates two packets, 21 a and 21 b, both beingsubjected to dielectrophoretic forces.

Dielectrophoretic forces may arise when a packet is placed in aninhomogeneous electrical field (AC or DC). In FIG. 2 the electricalfield is weaker on the left side than on the right side. An electricalfield induces electrical polarizations in the packet. The polarizationcharges are depicted at the two ends of the packets 21 a and 21 b alongthe field lines 35. Dielectrophoretic forces result from the interactionbetween the induced polarization (labeled as m₁ and m₂ in FIG. 2) andthe applied inhomogeneous field. If a packet is suspended in a mediumhaving different dielectric properties, such as a partitioning medium,then the packet may remain compartmentalized and may readily respond tomanipulation forces against viscous drag. In a field of non-uniformstrength, a packet may be directed towards either strong (packet 21 a)or weak (packet 21 b) electrical field regions, depending on whether thepacket is more (packet 21 a) or less (packet 21 b) polarizable than apartitioning medium. In a field of non-uniform phase distribution (i.e.a traveling electrical field), a packet may be directed towards fieldregions of larger or smaller phase distribution, depending whether thepacket has a longer or shorter dielectric response time than that of apartitioning medium.

DEP Theory

When a packet of radius r, suspended in an immiscible medium ofdifferent dielectric properties, is subjected to an electrical field offrequency f, the polarization of the packet can be represented using aneffective dipole moment (Wang et al., “A Unified Theory ofDielectrophoresis and Traveling Wave Dielectrophoresis”, Journal ofPhysics D: Applied Physics, Vol 27, pp. 1571-1574, 1994, incorporatedherein by reference){right arrow over (m)}(f)=4π∈_(m) r ³ P _(CM)(f){right arrow over(E)}(f)  (1)where {right arrow over (m)}(f) and {right arrow over (E)}(f) are thedipole moment and field vectors in the frequency domain, P_(CM)(f) isthe so-called Clausius-Mossotti factor, given byP _(CM)(f)=(∈*_(d)−∈*_(m))/(∈*_(d)+2∈*_(m)).  (2)

Here ∈*_(k)=∈_(k)−jσ_(k)/(2πf) are the complex permittivities of thepacket material (k=d) and its suspension medium (k=m), and ∈ and σ referto the dielectric permittivity and electrical conductivity,respectively. Using the effective dipole moment method, the DEP forcesacting on the packet are given by{right arrow over ( F )}(f)=2πr ³∈_(m)(Re[P(f)]∇E _((rms)) ² +Im[P(f)](E_(x0) ²∇φ_(x0) +E _(y0) ²∇φ_(y0) +E _(z0) ²∇φ_(z0)))  (3)where E(rms) is the RMS value of the field strength, E_(i0) and φ_(i0)(i=x; y;z) are the magnitude and phase, respectively, of the fieldcomponents in a Cartesian coordinate frame. Equation (3) shows that theDEP force contains two independent terms. The first, relating to thereal (in phase) part of the polarization factor Re[P(f)] and tonon-uniformities in the field magnitude (∇E_((rms)) ²). Depending on thesign of Re[P(f)], this force directs the packet either toward strong orweak field regions. The second term relates to the imaginary (out ofphase) part of the polarization factor (Im[P(f)]) and to field phasenon-uniformities (∇φ_(i0), i=x; y; z) that correspond to the fieldtraveling through space from large to small phase regions. Depending onthe sign of Im[P(f)], this directs packets toward regions where thephase values of the field components are larger or smaller.

Equations (1-3) indicate that the DEP phenomena have the followingcharacteristics:

(1) DEP forces experienced by packets are dependent on the dielectricproperties of the packets (∈*_(d)) and the partitioning medium (∈*_(m)).

(2) The strong dependence of three-dimensional DEP forces on the fieldconfiguration allows for versatility in implementing dielectrophoreticmanipulations.

DEP Forces on Packets

In one embodiment, a conventional dielectrophoresis component may beused for packet manipulation. In this case, the DEP force is given by{right arrow over ( F )}(f)=2πr ³∈_(m) Re[P(f)]∇E _((rms)) ²  (4)

where r is the packet radius, ∈_(m) is the dielectric permittivity ofthe suspending fluid. Re[P(f)] is the real (in phase) part of thepolarization factor and ∇E_((rms)) ² is the field non-uniformity factor.For packets of water (∈=78 and σ>10⁻⁴ S/m) suspended in a hydrocarbonfluid (∈=˜2 and σ˜0), the factor Re[P(f)] is always positive and closeto unity. Therefore, water packets are always attracted towards regionsof large field strength. For example, if an electrode array composed ofcircular electrodes arranged in a hexagonal fashion is provided, waterpackets may be dielectrophoretically moved towards and trapped between,for example, an electrode pair, over a single electrode, or above aplurality of electrodes to which electrical signals are applied.Switching the electrical signals may result in movement of the DEP trapsand may cause water packets to move in a chamber. Thus, packetmanipulation may be realized by switching electrical signals applied toan electrode array so that DEP field traps are made “mobile” within achamber.

Typical Forces and Velocities

For a water packet of 100 μm suspended in a hydrocarbon fluid such asdecane, the DEP force may be on the order of 1000 pN if the fieldnon-uniformity is 1.25×10¹³ V²/m³ (equivalent to 5V RMS applied to anelectrode pair of distance 50 μm with the field decaying to zero at 1000μm). If the viscosity of the hydrocarbon fluid is small (0.838 mPa forDecane), the packet velocity may be of the order of 600 μm/sec,indicating that fast manipulation of packets is possible with electrodearrays. In the above analysis, DEP force equation (4) has been used,which was developed for non-deformable particles and holds well forsuspended particles (such as cells, latex particles). Fluid packets maybe deformed under the influence of applied electrical field, affectingthe accuracy of equation (4) in describing DEP forces for packets.Nevertheless, equation (4) should be generally applicable with somepossible correction factors for different packet shapes.

FIG. 3 shows one possible implementation of position sensor 23 of FIG.2. Shown in FIG. 3 are five impedance sensing electrodes 19, hereillustrated as 19 a, 19 b, 19 c, 19 d, and 19 e. Each sensing electrode19 may be coupled to an impedance sensor 29, here illustrated asimpedance sensors 29 a, 29 b, 29 c, and 29 d. In one embodiment,impedance sensing electrodes 19 may be positioned in operativerelationship with surface 12 of fluidic device 10 in FIG. 1. Forinstance, sensing electrodes 19 may be placed on or near surface 12. Aspackets 21 are manipulated about surface 12 by the application ofappropriate manipulation forces, impedance sensing electrodes 19 andsensors 29 may sense a position of packets 21 by making one or moreimpedance measurements.

If the dielectric medium above an electrode is displaced by a packethaving different dielectric and/or conductive properties, the impedancedetected at the electrode element will change. Thus, one may determinethe position of packets 21 by noting the impedance measurementsassociated therewith. As is shown in FIG. 3, the impedance betweenimpedance sensing electrodes 19 a and 19 b is “high” (see impedancesensor 29 d) relative to, for instance, the impedance between impedancesensing electrodes 19 b and 19 c (see impedance sensor 29 c). Thus, bypre-determining that the “high” impedance value corresponds to theimpedance due to the partitioning medium, it may be deduced that somematerial of different impedance to the partitioning medium liessomewhere between impedance sensing electrodes 19 d and 19 e and between19 b and 19 c because the impedance associated with those electrodes is“low” (see impedance sensor 29 a). By like reasoning, one may assumethat no packet lies between impedance sensing electrodes 19 c and 19 d,for the impedance between those two electrodes is relatively “high” (seeimpedance sensor 29 b and 29 c).

Those of skill in the art will appreciate that the “low” and “high”values discussed above may be reversed, depending upon the relativeimpedances of a packet and of a suspending medium. In other words, insome situations, a relatively “high” impedance measurement may signalthe presence of a packet in between a pair of electrodes while arelatively “low” impedance may signal the lack of a packet. Those ofskill in the art will also appreciate that individual impedancemeasurements may exhibit a wide range of values (not just “low” or“high”), and it may be possible to characterize different types andsizes of materials by noting their associated impedance measurements.For instance, one may be able to differentiate, by type, the two packets21 of FIG. 3 by noting any differences in their impedance readings onimpedance sensors 29 a and 29 c.

Impedance sensing may be based on the so-called mixture theory, whichassociates the impedance of a heterogeneous system with the dielectricproperties of various system components and their volume fractions. Takea two-component, heterogeneous system where component 2 having complexdielectric permittivity

$\left( {{ɛ_{2}^{*} = {ɛ_{2} - {j\frac{\sigma_{2}}{2\;\pi\; f}}}},} \right.$f is the frequency) and a volume fraction a is suspended in component 1having complex dielectric permittivity

$\left( {ɛ_{1}^{*} = {ɛ_{1} - {j\frac{\sigma_{1}}{2\;\pi\; f}}}} \right).$The complex permittivity of the total system is given by (Wang et al.,“Theoretical and experimental investigations of the interdependence ofthe dielectric, dielectrophoretic and electrorotational behavior ofcolloidal particles” in J. Phys. D: Appl. Phys. 26: 312-322, 1993,incorporated herein by reference)

$ɛ_{sys}^{*} = {ɛ_{1}^{*}{\frac{\frac{1}{\alpha} + {2\frac{ɛ_{2}^{*} - ɛ_{1}^{*}}{ɛ_{2}^{*} + {2\; ɛ_{1}^{*}}}}}{\frac{1}{\alpha} - \frac{ɛ_{2}^{*} - ɛ_{1}^{*}}{ɛ_{2}^{*} + {2\; ɛ_{1}^{*}}}}.}}$

The total impedance of the system, which is assumed to have length L andcross-sectional area A, is given by

$\Omega = {\frac{L}{\omega\; ɛ_{sys}^{*}A}.}$

The electrical impedance between two electrode elements in the presenceor absence of a packet may be analyzed using the above equations, withthe parameters L and A determined experimentally. The existence of apacket may correspond to α>0 and the absence of a packet may correspondto α=0. From these equations, an impedance change would occur when apacket having different dielectric property (∈*₂) from the partitioningmedia (∈*₁) is introduced into the space between the two electrodeelements.

A relatively low impedance measurement may indicate an obstruction or apacket (as is illustrated in FIG. 3) on or near surface 12. Bydetermining impedance values, one may map locations of obstructions orpackets relative to surface 12. In this way, one may generate a packetand/or obstruction distribution map with respect to reaction surface 12of fluidic device 10. With the benefit of this disclosure, one of skillin the art will appreciate that the description associated with FIG. 3may be implemented in many different ways. In particular, one may useany suitable type of impedance measurement devices known in the art tofunction with one or more electrodes. Such devices may include animpedance analyzer, a DC/AC conductance meter, or any circuit based uponmethods of operation of these or other instruments having similarfunction.

FIG. 4 shows a three dimensional view of one embodiment of a fluidicdevice 10 according to the present disclosure. Fluidic device 10includes reaction surface 12, an inlet port 14, an outlet port 16,driving electrodes 18, impedance sensing electrodes 19, connectors 20,and wall 22.

Reaction surface 12 provides an interaction site for packets. In oneembodiment, reaction surface 12 may be completely or partially coveredwith a partitioning medium (not shown in FIG. 4) or other substance. Inone embodiment, reaction surface 12 may be coated. In particular, formanipulation of aqueous packets in a hydrophobic partitioning medium,reaction surface 12 may include a hydrophobic coating, or layer, havinga hydrophobicity similar to or greater than the hydrophobicity of thepartitioning medium. Such a coating may prevent an aqueous packet fromsticking, from spreading, or from becoming unstable upon contact withreaction surface 12. Additionally, a coating may modify associationand/or interaction forces between packets and reaction surfaces tofacilitate manipulation of packets by appropriate manipulation forces.Further, a coating may be used to reduce contamination of reactionsurfaces by reagents in packets. Still further, a coating may facilitatethe deliberate adhesion, wetting, or sensing of packets at or onreaction surfaces. If a dielectric layer coating is applied, the layershould be made sufficiently thin to allow AC electric field penetrationthrough the dielectric layer. In one embodiment, the thickness of thelayer may be between about 2 nm and about 1 micron. In one embodiment, ahydrophobic coating may be Teflon that may be applied by means known inthe art such as sputtering or spin-coating. It is to be understood thatany other suitable coating that modifies an interaction between packetsand the reaction surface may be used.

Reaction surface 12 may be formed from a number of suitable materials.In the illustrated embodiment, reaction surface 12 is a planar surfacethat has an upper surface including driving electrodes 18 and impedancesensing electrodes 19. Although illustrated as being coplanar withreaction surface 12, it is to be understood that driving electrodes 18and 19 may also be elevated or depressed with respect to reactionsurface 12. Likewise, reaction surface 12 need not be planar. Rather, itmay have concave or convex portions, or it may be deformed in some othermanner. Reaction surface 12 may be glass, silicon dioxide, a polymer, aceramic, or any suitable electrically insulating material. Thedimensions of reaction surface 12 may vary widely depending on theapplication but may be between about 20 microns by about 20 microns andabout 50 centimeters by about 50 centimeters. More particularly,reaction surface 12 may be between about 3 millimeters by about 3millimeters and about 30 centimeters by about 30 centimeters.

Inlet port 14 may be adapted to inject or introduce materials ontoreaction surface 12 and may be any structure allowing ingress toreaction surface 12. In the illustrated embodiment, inlet port 14consists of an opening in wall 22. Such an opening may be of anysuitable size or shape. Alternatively, inlet port 14 may be a syringeneedle a micropipette, a tube, an inkjet injector, or any other suitabledevice able to inject a material for introduction onto reaction surface12. Using a micropipette or equivalent device, wall 22 may not need toinclude any openings. Rather, material may be introduced onto reactionsurface 12 from above. A micropipette or any other equivalent device maybe attached to a micromanipulation stage (not shown in FIG. 4) so thatmaterial may be precisely deposited onto specific locations of reactionsurface 12. In one embodiment, inlet port 14 may consist of acylindrical tube opening onto reaction surface 12. Such a tube may havea diameter of between about 1 micrometer and about 1 mm and, moreparticularly, between about 10 and 100 microns.

Outlet port 16 may be adapted to collect packets of material fromreaction surface 12. Outlet port 16 may be any structure allowing egressfrom reaction surface 12. In the illustrated embodiment, outlet port 16consists of an opening in wall 22. The opening may be of any suitablesize or shape. Alternatively, outlet port 16 may be a micropipette orany other equivalent device able to collect a material from reactionsurface 12. Wall 22 may not need to include any openings. Rather,packets of material may be collected from reaction surface 12 fromabove. A syringe or any other equivalent device may be attached to amicromanipulation stage (not shown in FIG. 4) so that packets may beprecisely collected from specific locations on reaction surface 12. Inone embodiment, outlet port 16 may consist of a cylindrical tube openingonto reaction surface 12. Such a tube may have a diameter of about 1millimeter and a length of about 3 centimeters or longer.

In one embodiment, inlet port 14 and outlet port 16 may be integral. Forinstance, in the embodiment shown in FIG. 1 port 15 is a cylindricaltube opening onto reaction surface 12. In alternative embodiments, onemicropipette may serve as both an inlet port and an outlet port.Alternatively, a single opening in wall 22 may serve both input andoutput functions. In another embodiment, multiple inlet and outlet portsmay be utilized.

Fluidic device 10 may include an arbitrary number of inlet and outletports. For example, any one of the three unnumbered openings in wall 22,illustrated in FIG. 4, may serve as an inlet port, an outlet port, or anintegral inlet-outlet port, such as port 15 of FIG. 1. In anotherembodiment, multiple inlet and/or outlet ports may extend completely orpartially along a wall 22 so that materials may be introduced and/orcollected to and/or from reaction surface 12. In such an embodiment, onemay more precisely introduce or collect materials.

In FIG. 4, driving electrode 18 is one of a number of other drivingelectrodes arranged in an array upon reaction surface 12. In thisembodiment, driving electrodes 18 may be associated with force generator25 of FIG. 1, for the driving electrodes 18 may contribute to thegeneration of forces, such as forces F₁ and F₂ of FIG. 1, to manipulatepackets of material on reaction surface 12 to promote, for instance,microfluidic interactions.

Dielectrophoretic forces may be generated by an array of individualdriving electrodes 18 fabricated on an upper surface of a reactionsurface 12. The driving electrode elements 18 may be individuallyaddressable with AC or DC electrical signals. Applying an appropriatesignal to driving electrode 18 sets up an electrical field thatgenerates a dielectrophoretic force that acts upon a packet, known to beat a certain location through impedance measurements as described abovein relation to FIG. 3. Switching different signals to differentelectrodes sets up electrical field distributions within fluidic device10. Such electrical field distributions may be utilized to manipulatepackets in a partitioning medium.

In particular, the movement of packets under the influence of amanipulation force may be controlled by switching appropriate electricalsignals to different combinations of driving electrodes 18.Specifically, the switching of electrical signals may initiate differentfield distributions and generate manipulation forces that trap, repel,transport, or perform other manipulations upon packets of material. Byprogrammably switching electrical signals to different combinations ofdriving electrodes 18 within an array, electric field distributions andmanipulation forces acting upon packets may be programmable so thatpackets may be manipulated along arbitrarily chosen or predeterminedpaths in a partitioning medium along reaction surface 12. Thus, packetsmay be manipulated in an unlimited manner. Signals may be appropriatelyswitched to cause, for instance, a packet to move a single “unitdistance”—a distance between two neighboring electrodes. Further, byprogrammably switching electrical signals, different microfluidicreactions may be performed in series or in parallel. An electrode arrayhaving such an ability to utilize programmable dielectrophoretic forcesby programmed switching of electrical signals to different combinationsof driving electrodes 18 may be termed a programmable dielectrophoreticarray (PDA).

In FIG. 4, impedance sensing electrode 19 is one of a number of otherimpedance sensing electrodes arranged in an array upon reaction surface12. In this embodiment, impedance sensing electrodes 19 may beassociated with position sensor 23 of FIG. 1 and is illustrated in FIG.3. Impedance sensing electrodes 19 contribute to the sensing of packetpositions upon reaction surface 12 so that those packets of material maybe monitored and manipulated according to position.

In the illustrated embodiment, driving electrodes 18 and impedancesensing electrodes 19 are electrodes of a two dimensional electrodearray coupled to a top surface of reaction surface 12. The size of thearray may vary according to need, but in one embodiment a 16 by 16 arrayis employed. Because fluidic device 10 is scaleable, smaller or largerarrays may be fabricated without significant departure from the presentdisclosure. For example, 256 by 256 arrays or larger may be madeaccording to the present disclosure. Driving electrodes 18 and impedancesensing electrodes 19 within an array may be uniformly or non-uniformlyspaced. The spacing may vary widely, but in one embodiment, the spacingmay be between about 2 microns and about 200 microns. The electrodes mayhave different forms such as lines, squares, circles, diamonds,polygons, or other suitable shapes. The dimensions of each electrode mayvary, but a typical electrode may be between about 0.2 microns and about10 mm., and more particularly, between about 1 micron and about 200microns. Driving electrodes 18 and impedance sensing electrodes 19 maybe formed using any method known in the art. In one embodiment, suchelectrodes may be formed using standard photolithography techniques. Forexample, one may refer to, e.g., D. Qin et al, “Microfabrication,Microstructures and Microsystems”, Microsystem Technology in Chemistryand Life Sciences (Ed. Manz and Becker), Springer, Berlin, 1997, pp1-20, which is incorporated herein by reference. Also, one may refer toMadou, Fundamentals of Microfabrication, CRC Press, Boca Raton, 1997,which is incorporated herein by reference. Depending upon the particularapplication, and the nature of the packets and partitioning medium, thesize and spacing of electrodes 18 and 19 may be smaller than, of similarsize, or larger than the diameters of the packets.

In one embodiment, impedance sensing electrodes 19 may be integral withdriving electrodes 18. In such an embodiment, the resulting array may betermed an integral array. With an integral array, a single conductorcoupled to reaction surface 12 may serve both purposes—driving packetsand sensing positions of packets. Thus, a programmable manipulationforce may be generated upon packets upon reaction surface 12 and aposition of those packets may be sensed with a single electrode array.

In the embodiment of FIG. 4, wall 22 is adapted to enclose one or moresides of reaction surface 12. It is to be understood that wall 22 may beany suitable structure capable of enclosing one or more sides and/or thetop of reaction surface 12. As illustrated, wall 22 encloses four sidesof reaction surface 12, defining an open reaction surface chamber. In amost typical embodiment, the chamber may have a thickness of betweenabout 10 microns and about 20 millimeters. In another embodiment, wall22 may enclose the top of reaction surface 12, forming a closed reactionchamber.

Wall 22 may be formed from any suitable material. In one embodiment,wall 22 may be made from machined plastic, aluminum, glass, plastic,ceramic, or any combination thereof. In one embodiment, wall 22 may bepartially or completely transparent to certain wavelengths of radiation.Thus, radiation may be transmitted through wall 22 to initiate ormaintain certain microfluidic reactions or processes for sensing. Forinstance, a photochemical reaction may be initiated through wall 22.

Connectors 20 of FIG. 4 may be adapted to provide electrical connectionsto driving electrodes 18 and to impedance sensing electrodes 19.Connectors 20 may provide electrical connections to an entire array ofelectrodes, or to preselected ones or groups. In one embodiment,connectors 20 are coupled to a controller (not shown in FIG. 4) that mayadjust a programmable manipulation force distribution generated bydriving electrodes 18 according one or more packets position sensed withimpedance sensing electrodes 19. Thus, such a controller may effectivelyprovide a feedback mechanism between the driving electrodes 18 and theimpedance sensing electrodes 19—The signals applied to drivingelectrodes 18 may be adjusted in view of one or more results from theimpedance sensing electrodes 19.

Turning now to FIG. 5, there is shown a side cross section view of afluidic device 10 according to the present disclosure. Fluidic device 10includes a reaction chamber 41 and an array of integral impedancesensing and driving electrodes, integral array 43. In the illustratedembodiment, a control chip 60 is coupled to integral array 43.Positioned upon a top surface of control chip 60 may be capillary wall62 that forms a lower surface of a capillary 64. Capillary 64 may leadto an inlet port 14 that leads into chamber 41. Although illustratedwith only one inlet port, it is contemplated that there may be severalsuch ports providing access to chamber 41. Above capillary 64 is asubstrate 66 that, in one embodiment, is made of glass although anysuitable material known in the art may be utilized instead.

In one embodiment, control chip 60 may be an integrated circuitconfigured to control integrated array 43. Alternatively, control chip60 may be a control interface leading to another controlling device suchas an integrated circuit, computer, or similar device that may controlintegral array 43. Control chip 60 may utilize flip-chip technology orany other suitable technique to establish electrical control overintegral array 43 by switching different signals to and from it.

FIG. 6 shows a controller 81 according to one embodiment of thepresently disclosed method and apparatus. Controller 81 may include acomputer 80, a signal generator 82, an electrode selector 84, atransducer 88, and a fluidic device 10 having a driving electrode 18 andan impedance sensing electrode 19.

Computer 80 may be configured to control fluidic device 10 and the fluidprocessing occurring upon reaction surface 12. Computer 80 may have auser interface that allows for simple programming of signal generator 82and transducer 88, which measures impedance, to allow for programmablemicrofluidic processing. In particular, computer 80 may programmablycontrol the initiation/termination of one or more signals from signalgenerator 82, the parameters of the one or more signals includingfrequencies, voltages, and particular waveforms, and control theswitching of one or more signals from generator 82 to differentcombinations of electrodes 18 and 19.

Computer 80 may vary signals in many ways. For instance, one signalhaving a first frequency component may be sent through electrodeselector 84 to a driving electrode 18 while another signal having asecond, different frequency component may be sent to, for instance, animpedance sensing electrode 19 and through electrode selector 84. Anysequence of signals or combinations of signals may be sent differentcombinations of electrodes and from the fluidic device 10. Any signalparameter may be varied and any electrode selection may be controlled sothat appropriate electric fields may be established at particularlocations upon reaction surface 12. Alternating Current or DirectCurrent signals may be utilized.

Signal generator 82 may send a driving signal to one or more drivingelectrodes 18 while sending a sensing signal to one or more impedancesensing electrodes 19. In one embodiment, the driving signal and thesensing signal may comprise a single, composite processing signal havingdifferent frequency components. Such a signal may be used with anintegrated array to provide (via a single processing signal) a frequencycomponent to generate a programmable manipulation force and a frequencycomponent to provide an impedance sensing signal. The manipulation andimpedance sensing components may also be combined by multiplexing orswitching in time as is known in the art.

In one embodiment, signal generator 82 provides one or more programmabledriving signals to one or more driving electrodes 18 through electrodeselector 84 so that a programmable alternating-current electric field,such as a non-uniform field, may be produced at reaction surface 12.That electric field may induce polarization of packets of materialsadjacent to or in the vicinity of the one or more driving electrodes 18.A programmable dielectrophoretic force distribution may, in this manner,be generated that manipulates packets in a controllable, programmablemanner so that varied programmable fluidic interactions may take placeupon reaction surface 12.

In one embodiment, signal generator 82 provides a sensing signal to oneor more impedance sensing electrodes 19 so that an impedance measurementmay be made. The impedance sensing signal may be applied to one or morepairs of impedance sensing electrodes 19 and a change in voltage orcurrent may be detected and transmitted to computer 80 via sensingelectrodes 88 and wire 86. Computer 80 may then compute the impedanceand hence, determine whether a packet or obstruction was present at ornear the pair(s) of impedance sensing electrodes 19 being probed.

In an embodiment utilizing a single integrated array (instead ofseparate impedance sensing and driving electrode arrays, an integratedarray utilizes electrodes that function to both drive and sensepackets), the integrated array may both generate a programmablemanipulation force and sense an impedance. In one approach, electricalsensing signals for sensing electrode impedance may be applied atdifferent frequencies from driving signals for manipulation of packets.Summing signal amplifiers (not shown) may be used to combine signalsfrom sensing and driving electronics. By using a frequency filternetwork (not shown), electrode impedance sensing signals may be isolatedfrom the driving signals. For example, a constant current at sensingfrequency f_(s) may be applied to integrated electrode pairs to bemeasured. The sensing electronics 88, may then be operated at only theapplied frequency f_(s) to determine a voltage drops across theintegrated electrode pairs, thus allowing the impedance at the sensingfrequency f_(s) to be derived without interference from the drivingsignals.

In another embodiment, driving signals may be used to monitor electricalimpedance directly. Driving signals may be switched to one or moreintegrated electrodes to generate a force to manipulate or interactpackets upon a reaction surface. Simultaneously, an electrical currentsensing circuit may be used to measure electrical current going throughthe energized integrated electrodes. Electrode impedances may be derivedfrom such measurements of electrical current.

Although any suitable device may be used, in one embodiment a functiongenerator is used as signal generator 82. More particularly, anarbitrary waveform signal generator in combination with voltage or poweramplifies or a transformer may be used to generate the requiredvoltages. In one embodiment, signal generator 82 may provide n sine-wavesignals having a frequency up to the range of GHz and more particularlybetween about 1 kHz and about 10 MHz and a voltage between about 1 Vpeak-to-peak and about 1000 V peak-to-peak, and more particularly,between about 10 V peak-to-peak and about 100 V peak-to-peak.

As illustrated, signal generator 82 may be connected to an electrodeselector 84. Electrode selector 84 may apply one or more signals fromsignal generator 82 to one or more individual electrodes (impedancesensing electrodes and/or driving electrodes may be individuallyaddressable). Electrode selector 84 may be one of a number of suitabledevices including a switch, a multiplexer, or the like. Alternatively,electrode selector 84 may apply one or more signals to one or moregroups of electrodes. In one embodiment, selector 84 is made ofelectronic switches or a multiplexer. Selector 84 may be digitallycontrolled. With the benefit of this disclosure, those of skill in theart will understand that selector 84 may be any suitable device that mayprogrammably divert one or more signals to one or more electrodes in anyarbitrary manner.

As illustrated in FIG. 6, controller 81 provides a feedback loopmechanism from impedance sensing electrodes 19 to driving electrodes 18via computer 80, which itself is coupled to signal generator 82,selector 84, and transducer 88. With the benefit of the presentdisclosure, those of skill in the art will recognize that controller 81may contain more or fewer components. The feedback mechanism allowscomputer 80 to tailor its commands to signal generator 82 according topositions of packets upon reaction surface 12, as determined byimpedance sensing electrodes 19. Thus, controller 81 allows for theadjustment of driving signals (and hence the adjustment of programmablemanipulation forces) according to positions of packets (as determined byimpedance sensing electrodes 19). In embodiments utilizing an integralarray of electrodes having integral impedance sensing electrodes 19 anddriving electrodes 18, a feedback mechanism may operate as follows.Positions of packets may be determined by measuring impedances betweenelectrical elements by applying impedance sensing signals to theintegral array. Position information may then be used to control drivingsignals to the integral array to perform microfluidic processing throughthe manipulation of packets. In one embodiment computer 80 may bereplaced by an application specific integrated circuit controller (ASIC)designed specifically for the purpose.

FIG. 7 shows an electrode driver 94 according to an embodiment of thepresently disclosed method and apparatus. Driver 94 includes a computer80, a signal generator 82, a resistor network 100, a switching network104, and a bitmap 108. Driver 94 is coupled to fluidic device 10 whichincludes reaction surface 12 and an integral array 43.

Driver 94 may assist in the application of signals to integral array 43in order to direct microfluidic interactions of packets of material uponreaction surface 12. In one embodiment, computer 80 directs signalgenerator 82 to apply an AC signal to integral array 43. In theillustrated embodiment, from signal generator 82 there may be provided,for example, eight increasing voltage amplitudes using resistor network100, although more or fewer voltage amplitudes may be used. The eight ACsignals may be distributed by switching network 104 via connection 106to the integral array 43 according to a bitmap 108 or according to anyother suitable data structure stored in computer 80 or in anotherdevice. By modifying bitmap 108 via computer 80, different voltageamplitudes may be applied to different electrodes.

In one embodiment, signals to each electrode of integral array 43 may berepresented in bitmap 108 by 3 bits to address eight available voltageamplitudes. Voltage amplitude distributions of bitmap 108 may betransmitted sequentially to switching network 104 via connection 110twelve bits at a time using a communication protocol as is known in theart. In one embodiment, the communication protocol may use the followingconvention. To address a single electrode of integral array 43, thefirst four bits may specify the row of the array. The second four bitsmay specify the column of the array. The next three bits may specify thedesired voltage to be applied. The last bit may be used for errorcontrol by parity check. The rows/column arrangement may be used fordifferent layouts of arrays. For instance, the row/column convention ofaddressing may be used even for a hexagonal grid array configuration.Those skilled in the art will appreciate that other methods may be usedto address the electronic switching network 104 from computer 80.

FIG. 8 is side cross-section view of one embodiment of a fluidic device10. Fluidic device 10 includes a wall 22 which encloses the sides andtop of a reaction surface 12 to form a reaction chamber 41. Reactionsurface 12 includes an integral array 43. Coupled to the integral arraymay be an interface board 54. Interface board 54 may interface theintegral array 43 with integrated circuits 50 via interconnect 55 andsolder bumps 52.

In the embodiment of FIG. 8, interface board 54 may be sandwichedbetween chamber 41 and integrated circuits 50. On one side, interfaceboard 54 may provide electrical signals (AC or DC) to electrodes ofintegral array 43, while the other side of interface board 54 mayinclude pads for flip-chip mounting of integrated circuits 50.Intermediate layers of interface board 54 may contain electrical leads,interconnects and vias, such as interconnect 55 to transfer power andsignals to and from electrodes of integral array 43 and integratedcircuits 50.

Interface board 54 may be fabricated using suitable PC-board and flipchip technologies as is known in the art. Suitable silk-screened orelectroplated flip-chip solder bump techniques may likewise be used.Alternatively, ink-jet solder deposition may be used as is known in theart.

FIG. 9 is a top view of an embodiment of a fluidic device 10. In theillustrated embodiment, fluidic device 10 is made up of four distinct 8by 8 integral arrays 43, forming a 16 by 16 array. Under each 8 by 8array may be situated an integrated circuit (not shown in FIG. 9) thatmay provide control and signal processing to electrodes of the integralarray 43. The integral arrays may be coupled to a circuit conducting pad34 that may be coupled to an interface conducting pad 36 by a bond wire38 (shown only in one quadrant). Connected to interface conducting pad36 may be wire 42, or another suitable connector such as a PC boardconnector, leading to a computer or other suitable controlling device.

FIG. 9B is another top view of an embodiment of a fluidic device 10. Inthis embodiment, many ports 15 are situated along edges of fluidicdevice 10. These ports 15 may serve to inject and/or collect packets 21to/from reaction surface 12. Also illustrated is a sensor 122 positionedadjacent a port 15. Such a sensor is described in reference to FIG. 10below.

FIG. 10 is a block diagram of a microfluidic processing system 115.Processing system 115 may be designed to allow for control ofprogrammable dielectrophoretic array (PDA) 116 that serves as the sitefor microfluidic interactions and may be constructed in accordance withthe present disclosure. In view of its broad functionality, PDA 116 mayserve a role, in the field of fluidic processing, analogous to the roleplayed by a Central Processing Unit in the field of computers.

Coupled to PDA 116 are fluidic sensors 122. Fluidic sensors 122 maymeasure and monitor fluid products from, in, or on PDA 116. Forinstance, fluidic sensors 122 may measure and identify reaction productsand may quantify reactions between packets. In one embodiment, fluidicsensors 122 may include an optical microscope or one or more sensors(chemical, electrochemical, electrical, optical, or the like), but anyother suitable monitoring device known in the art may be substitutedtherewith. For example, fluidic sensors 122 may be an electrochemicalsensor that monitors the presence and concentration of electroactive(redox-active) molecules in a packet solution. An electrochemical sensormay take the form of two or more microelectrodes. In a three-electrodeconfiguration, for example, electrodes may correspond to working,reference, and counter electrodes. A packet to be analyzed may be movedto be in contact with the three electrodes. A voltage signal may beapplied between the working and reference electrode, and the currentbetween the working and counter electrode may be monitored. Thevoltage-current relationship allows for the determination of thepresence or absence, and concentration of electro-active molecules inthe packet solution. Also attached to PDA 116 may be suitable materialinjection and extraction devices 120 coupled to appropriate inlet oroutlet ports of PDA 116 (not shown in FIG. 10). Such devices may be anysuitable structure allowing ingress to and egress from PDA 116.

In electrical communication with PDA 116 may be PDA voltage drivers 126and dielectric position sensors 124. PDA voltage drivers 126 may beadapted to drive electrodes within PDA 116 so that an electric field maybe established that sets up manipulation forces that manipulate one ormore packets of material within PDA 116 to promote microfluidicinteractions. In one embodiment, PDA voltage drivers 126 may include asignal generator and switching network as described in relation to FIG.7. Dielectric position sensors 124 may measure positions of packetswithin PDA 116. In one embodiment, dielectric position sensors 124 mayinclude measuring devices connected to appropriate sensors that maydetermine a position of one or more packets of material by sensing, forinstance, a change in impedance between neighboring impedance sensingelectrodes within PDA 116 and by correlating that change in impedancewith a packet positioned adjacent the neighboring sensors according tothe teachings of the present disclosure.

Coupled to packet injection and extraction devices 120, PDA voltagedrivers 126, and dielectric position sensors 124 may be computerinterface 128. Computer interface 128 may be configured to allow hostcomputer 130 to interact with PDA 116. In one embodiment, computerinterface 128 may be a digital or analog card or board that may analyzeimpedance data to obtain a packet distribution map.

In the embodiment of FIG. 10, host computer 130 may be coupled tocomputer interface 128 to provide for control of PDA 116. Host computer130 may be coupled to position tracking agent 132 and to low-levelcontrol agent 134. Position tracking agent 132 may be adapted to store,process, and track positions of packets within the fluidic processor PDA116. Low-level control agent 134 may be configured to provideinstructions to host computer 130 from library interface 136 andsoftware interface 138. Library interface 136 may hold various sets ofsubroutines for programmably manipulating packets of materials on PDA116. Software interface 138 that may allow for custom programming ofinstructions to be executed by the fluidic processor PDA 116 toprogrammably manipulate packets. Alternatively established programs ofmanipulation instructions for specific fluid processing tests may beread from stored data and executed by the PDA fluid processor 116.

FIG. 11 illustrates operation of the presently disclosed method andapparatus. In FIG. 11, open squares represent electrodes of an integralarray. However, it is contemplated that the description below appliesequally well to a device utilizing separate impedance sensing electrodesand driving electrodes.

In the illustrated embodiment, a packet 21 a may be introduced ontoreaction surface 12 adjacent the location represented by integralimpedance sensor/electrode 201. The packet may be compartmentalized inan immiscible partitioning medium (not shown). The introduction of thepacket may be accomplished using an appropriate inlet port positionedadjacent to electrode 201. Alternatively, a packet may be introducedadjacent electrode 201 by applying an appropriate signal to electrode201 to generate an extraction force that may extract the packet from aninlet port or from an injector directly onto reaction surface 12 andadjacent to electrode 201.

Once positioned upon reaction surface 12, packet 21 a may be made tomove along a predetermined path indicated by dashed line 250. A path maybe specified in a number of different ways. In one embodiment, a usermay specifically define a path. For instance, one may specify a path,through appropriate programming of a controller or processing system,such as the one depicted numeral 250. Alternatively, a user may specifya starting position and an ending position to define a path. Forinstance, a user may specify that packet 21 a is to be introducedadjacent electrode 201 and end at a location adjacent electrode 215.Alternatively, one may specify a starting and ending location withspecific path information in between. For instance, a user may specify astarting position, an ending position, and a wavy path in between. Ascan be seen from FIG. 11, the path may have any arbitrary shape and itmay be programmed in any number of ways.

To move packet 21 a generally along the path, electrical signals may besuitably switched to integral impedance sensors/electrode pairs so thatprogrammable manipulation forces may be created that act upon packet 21a to propel it generally along the specified path. As discussed earlier,the signals may be varied in numerous ways to achieve the propermanipulation force. In the illustrated embodiment, applying voltagesignals to electrode pairs 202 and 203 may create an attractivedielectrophoretic force that moves packet 21 a from electrode 201towards electrode 203 generally along path 250. As packet 21 a movesgenerally along a specified path, the integral array may measureimpedances to map the position of the packet upon reaction surface 12.Knowing the position of a packet allows manipulation forces to bedirected at appropriate positions to achieve a desired microfluidicprocessing task or interaction. In particular, knowing a position of apacket allows an appropriate signal to be switched to an appropriateelectrode or electrode pair to generate a manipulation force thatfurther propels or interacts the packet according to one or moreinstructions.

As packet 21 a moves from electrode 201 towards electrode 203, theimpedance between electrode 202 and electrode 203 may change value,indicating that packet 21 a is between, or partially between, those twoelectrodes. The impedance may be measured as described in FIG. 3. Acontroller or processing system (not shown in FIG. 11) may register thelocation of packet 21 a and may apply a signal, for instance, toelectrode pairs 204 and 205, creating an attractive dielectrophoreticforce which propels packet 21 a towards those electrodes generally alongpath 250. As the impedance between electrode 204 and electrode 205changes value, a controller or processing system may apply a signal toelectrodes 206 and 207 to propel packet 21 a along path 250. As packet21 a continues along path 250, the impedance between electrode 206 andelectrode 207 may change value, indicating the presence of packet 21 aadjacent that location along the array. Thus, as packet 21 a moves alongpath 250, a controller or processing system may constantly monitor theposition of the packet by measuring impedance between electrode pairsand adjust electrical signals to an appropriate electrode or electrodepair (and hence, adjust manipulation forces) to continue to propel thepacket further along the specified path.

Measuring an impedance between pairs of electrodes not only allows aposition of a packet to be determined, but it also allows for thedetermination of a location of an obstruction or blockage upon reactionsurface 12. For example, measuring the impedance between electrodes 211and 213 may indicate the presence of obstruction 212. By noting theposition of obstruction 212, a controller or processing system mayre-route one or more packets around the obstruction so that nointerference with microfluidic processing interactions occurs. Forexample, if a path is specified that passes through an area occupied byobstruction 212, a controller or processing system may modify electricalsignals to propel a packet generally along the specified path whileavoiding the obstruction. For instance, a stronger or weaker signal maybe sent to one or more electrodes or electrode pairs near obstruction212 to steer a packet clear of the blockage while still maintaining,generally, the path that was originally specified, and moreparticularly, the originally specified end point

A controller or processing system according to the presently disclosedmethod and apparatus may be programmed to scan for several obstructionsand/or packets. Such a scan may build up a distribution map, showing thelocation(s) of various packets and/or obstructions on an entire reactionsurface 12 or a portion thereof. Such a distribution map may be avirtual map, stored, for example, in a computer memory or display.Turning again to FIG. 11, impedances of all electrode pairs adjacent topath 250 may be measured to determine if an obstruction blocks that pathor if a packet lies somewhere in that area. If the path is determined tobe clear (e.g., if all the electrode pairs show an impedance valueindicating a clear area), a packet may be safely propelled generallyalong the path while avoiding any interactions with other packets and/orobstructions. However, if an obstruction is discovered, severaldifferent actions may be taken. In one embodiment, the user may benotified that a blockage exists along the specified path. The user maythen specify a different path or give another appropriate instruction.In another embodiment, the controller or processing system may determineif the obstruction may be avoided while still maintaining generally thesame specified path. If possible, electrical signals may be modified anddelivered to an electrode or electrode pairs to generate appropriateelectrical field distributions that set up proper manipulation forcesthat will aid in avoiding the obstruction. Because, at least in part, ofthis ability to constantly measure positions and responses of packetsduring manipulation, a controller or processing system may be capable ofmonitoring the integrity of fluidic processing, reporting and correctingany errors that may occur.

FIG. 11 also depicts how processing may be carried out on two packets.In the illustrated embodiment, a second packet 21 b begins on reactionsurface 12 near electrode 217. A second path, path 260, may be specifiedthat ends at electrode 219. As can be seen, paths 250 and 260 may crossat interaction point 240. At interaction point 240, the two packets mayinteract in many ways as illustrated, for example, in FIG. 12. Theinteraction may include, but is not limited to, fusing, merging, mixing,reacting, dividing, splitting, or any combination thereof. For instance,the two packets may interact at interaction point 240 to form one ormore intermediate or final reaction products. Those products may bemanipulated in the same or in a similar manner as the two originalpackets were manipulated.

FIG. 11 also depicts how maintenance may be performed upon reactionsurface 12. A maintenance packet 21 c adapted to perform maintenanceupon reaction surface 12 may be introduced onto reaction surface 12 by amaintenance port (not shown in FIG. 11). A maintenance port may besimilar to an inlet port in structure but may be dedicated to theintroduction of one or more maintenance packets 21 c designedspecifically, for instance, to clean or maintain reaction surface 12, asurface coating, or one or more electrodes or sensors. Maintenancepacket 21 c may also react with an obstruction in such a way as toremove that obstruction. As illustrated, maintenance packet 21 c maybegin near electrode 241. It may then be propelled along path 270,providing maintenance, perhaps, to electrodes 242 and 243. Maintenancepacket 21 c may be propelled back to a maintenance port, extracted fromreaction surface 12, and later used again, or it may discarded at anoutlet part.

FIG. 12 demonstrates several different possible fluidic interactionsthat may be carried out using the presently disclosed method andapparatus. In the illustrated embodiment, packets 21 (only one islabeled for convenience) reside upon a reaction surface 12 having anintegral array 43 (only one electrode is labeled for convenience). Inthe top pane of FIG. 12, there is shown an interaction in which a singlepacket is manipulated on the reaction surface by moving the packet in aprogrammed fashion. In the middle pane, two packets, starting atdifferent locations upon the reaction surface, are directed, viaappropriate electrical signals, to come together at a specified location(near the center of the array) to fuse together, for example, toinitiate a reaction. The fused packet may be manipulated just as theoriginal packets were manipulated. For instance, the fused packet may bemoved to various locations or it may fuse again with another packet(s).Shown in the bottom pane of FIG. 12 is a splitting interaction. Asshown, a single packet is subjected to different programmablemanipulation forces that cause the packet to split into two distinctpackets. Such an interaction may be accomplished by, first, noting theposition of the packet to be split, and then by applying appropriatesignals to electrode pairs to generate two or more opposing forces thatcause the packet to split apart.

FIG. 13 is a flowchart showing one embodiment of a method of operation.A material may be introduced onto a reaction surface andcompartmentalized to form one or more packets in step 300. Multiplematerials may be introduced at different locations along reactionsurface 12 to form a plurality of packets. A path may be specified as instep 310. The path may be designed to accomplish any type ofmicrofluidic processing, manipulation, or interaction. Differentreactions may be performed in serial or in parallel according todifferent paths. Instructions governing such processing may be embodiedin the pseudo-code that may be routed through computer interface 128 ofFIG. 10. Illustrative code may read as follows:

EXAMPLE AvidinActin.PSL

Use inlet(1-3), outlet(1-2) Inlet(1) is actin Inlet(2) is avidinInlet(3) is enzyme Outlet(1) is polymer Outlet(2) is waste Matrix(1,2)is accumulator Clean Do Sactin = (Pull actin) // pull a new packet onthe next Savidin = (Pull avidin) // available matrix element next toSenzyme = (Pull enzyme) // the inlets Move Sactin into accumulator //merges components and enzyme Move Savidin into accumulator // in asingle packet Move Senzyme into accumulator Wait 1000ms ShiftRowaccumulator.row ,+1 // drag packet left into polymer outlet Move0.5*accumulator into (2, accumulator.column) // drag half packet to row2 ShiftRow 2, + 1 // drag packet left into waste Loop Untilpolymer.count = 10 // number of packet at polymer outlet = 10 Clean

In step 315, computer 80 of FIG. 6 or any other suitable device maydetermine the next unit step along the path specified in step 315. Inother words, a path may be broken down into unit steps and the next unitstep or steps may be determined with respect to the specified path. Instep 320, a programmable manipulation force is generated on reactionsurface 12 through the use of any of the mechanisms disclosed herein.The programmable manipulation force may manipulate the one or morepackets according to instructions from a user. In step 330, theresponse(s) of the one or more packets may be monitored. This step mayinclude measuring an impedance on the reaction surface as discussedherein. In particular, one may determine whether the one or more packetsmoved to where they were supposed to, or whether they interacted asinstructed. In step 340, it may be determined if the packet movement wassuccessful—that is, it may be determined whether the packet ended up ata location corresponding to the unit step determined in step 315.

If a packet movement was successful (i.e., if the packet respondedcorrectly to the programmable manipulation force(s)), then it may bedetermined, by comparison with the specified path, whether or not thepacket destination has been reached. In other words, it may bedetermined if the packet has moved to the end location of the specifiedpath. If the destination has not been reached, the next unit stepmovement may be determined at step 315 and steps 320, 330, 340, and 365may be repeated. If the destination has been reached, it may bedetermined whether another packet is to be manipulated in step 370. Thisstep may include a user prompt. If no further packets are to bemanipulated, it may be determined whether fluidic processing is completein step 380. If yes, the process may be ended at step 390. Step 390 mayinclude the collecting of one or more packets, further analysis,throwing away of the reaction surface, or any procedure describedherein. If the processing is not complete, the next step of processingmay be determined in step 395. The next step may entail, for example,the introduction of another packet, the specification of another path,or any other step of FIG. 13.

If a packet manipulation is unsuccessful (i.e., if the appliedprogrammable manipulation force(s) did not produce a desired interactionor movement along a specified path as indicated by step 340), one maylocate an obstruction upon the reaction surface as indicated in step 350and as taught herein. After locating any obstructions, a new, modifiedpath may be determined or specified as indicated by step 360, leading tostep 310.

As mentioned with relation to FIG. 1, the present disclosurecontemplates that many different types of forces may be utilized as amanipulation force for promoting fluidic interactions among packets ofmaterial on a reaction surface. Specifically, suitable forces other thandielectrophoresis include electrophoretic forces, optical forces,mechanical forces, or any combination thereof. Below are discussedembodiments of the present disclosure dealing with electrophoretic andoptical manipulation forces.

Programmable Electrophoretic Array (PEA)

A fluidic processing system incorporating a programmable electrophoreticarray may be constructed according to the present disclosure. As usedherein, “programmable electrophoretic array” (PEA) refers to anelectrode array whose individual elements can be addressed with DC,pulsed, or low frequency AC electrical signals (typically, less thanabout 10 kHz) electrical signals. The addressing of electrode elementswith electrical signals initiates different field distributions andgenerates electrophoretic manipulation forces that trap, repel,transport or perform other manipulations upon charged packets on andabove the electrode plane. By programmably addressing electrode elementswithin the array with electrical signals, electric field distributionsand electrophoretic manipulation forces acting upon charged packets maybe programmable so that packets may be manipulated along arbitrarilychosen or predetermined paths. A PEA may utilize electrophoretic forcesin DC or low-frequency (typically, less than about 10 kHz) AC electricalfields. Such electrophoretic forces may be used instead of, or inaddition to, another manipulation forces such as dielectrophoresis.

Negative or positive charges may be induced or injected into fluidpackets. The charged packets may be moved or manipulated byelectrophoretic forces generated by an electrode array fabricated on aninner surfaces of a chamber in accordance with this disclosure. Theelectrode array, termed a programmable electrophoretic array (PEA), mayconsist of uniformly or non-uniformly spaced electrode elements.Individual electrode elements may be independently addressable with DC,pulsed, or low frequency AC electrical signals (< about 10 kHz).Characteristic dimensions of individual electrode elements may be of anysize but, in one embodiment, may lie between 0.2 micron and 10 mm.Individual electrode elements may take similar or different geometricalforms such as squares, circles, diamonds, or other shapes. Programmablyswitchable electrical signals may be applied to individual electrodeelements so that a programmable electrical field distribution may begenerated. Such a distribution may impose electrophoretic forces totrap, repel, transport or manipulate charged packets in a partitioningmedium. Further, electrical signals may be applied to such an array sothat a packet may be broken down to two or more packets. Theprogrammability of a PEA may be reflected in the fact that the electricfield distributions and electrophoretic forces acting on charged packetsmay be programmable so that charged packets may be trapped or repelledor transported along arbitrarily chosen paths in the partitioningmedium, and that a PEA may be programmed to perform different reactionsin series or in parallel where different manipulation protocols ofpackets (differing in size, number, and/or reagent type concentration)may be required. As with PDA surface modification, if a dielectric layercoating is applied to the surface of a PEA to modify interaction forcesbetween packets reaction surfaces, the dielectric layer may be madesufficiently thin (typically 2 nm to 1 micron) to allow for electricfield penetration.

Optical Manipulation

Optical tweezers (which may consist of a focused laser beam with a lightintensity gradient) may be also be used for trapping and manipulatingpackets of material. Optical manipulation requires that the refractiveindices of the packets be different from that of their suspendingmedium, for instance, a partitioning medium as described herein. Aslight passes through one or more packets, it may induce fluctuatingdipoles. Those dipoles may interact with electromagnetic fieldgradients, resulting in optical forces directed towards or away from thebrighter region of the light. If their refractive indices are higherthan that of the partitioning medium, packets may be trapped in a brightregion, and when the laser light moves with respect to the partitioningmedium, packets may follow the light beam, allowing for opticalmanipulation forces. Conversely, if the packets have refractive indicessmaller than their partitioning medium, they will experience forcesdirecting them away from bright regions.

Therefore, if packets have different refractive indexes from that of thepartitioning medium (e.g., water packets in air or oil), opticaltweezers may exert forces on them. Therefore, to manipulate and interactpackets, a microscope or other optical system incorporating one or morelaser tweezers may be used. A chamber containing a partitioning mediumin accordance with the present disclosure may be placed into such anoptical system. Following the introduction of packets of material intothe chamber, laser tweezers may be used to trap packets. By moving thefocal point of the optical tweezers with respect to the partitioningmedium (e.g., moving a stage holding the thin chamber containing thepartitioning medium whilst fixing the position of laser tweezers and/orby focusing the laser beam to different depths in the partitioningmedium), packets may be manipulated as described herein. Through the useof apparatus such as a computer-controllable, multi-axis translationstage, the movement of the optical tweezers with respect to thesuspending medium may be programmed or automatically controlled. Thusthe optical tweezer may be moved, with respect to the medium, along anyarbitrarily chosen or predetermined paths. By doing so, packets underthe influences of the optical tweezers may be manipulated along anyarbitrarily chosen or predetermined paths.

Example 1

Aqueous materials have been compartmentalized to form packets usinghydrophobic liquids as a partitioning medium. Partitioning mediums soused have included decane, bromodocane, mineral oil, and 3 in 1™ oil.Packets have been formed by briefly sonicating about 3 milliliters ofthe hydrophobic liquid to which had been added 20 to 50 microliters ofaqueous medium. Aqueous media tested have included deionized water, tapwater (electrical conductivity of about 40 mS/m) and phosphate bufferedsaline (PBS) solution.

Example 2

Aqueous packets suspended in mineral oil, bromodoecane and 3 in 1™ oilhave been collected by dielectrophoresis by applying sinusoidal signalsto gold-on-glass electrode arrays having 20, 80 and 160 micron spacing,respectively. The 20-micron electrode array consisted of parallel lineelectrodes (20 microns in width and spacing). The 80 and 160 micronelectrode arrays were of the interdigitated, castellated geometries.Aqueous packets were collected at electrode edges or tips when ACvoltage signals between 100 Hz and 20 MHz were applied. Applied voltageswere from 10 to 100 V peak-to-peak. The formation of pearl-chains ofwater packets has also been observed.

Example 3

Aqueous packets in hydrophobic suspension have been brought together andfused under the influence of dielectrophoretic forces on the sameelectrode arrays used in Example 2.

Example 4

Packets have been moved from one electrode element to another underinfluence of dielectrophoretic forces when the AC electrical field isswitched on an addressable array of parallel line electrodes having 20micron width and spacing.

Example 5

Sensitive AC impedance monitors have been built for use withmicroelectrode arrays. Such monitors may provide for sensitivedielectric sensing of packet positions.

While the present disclosure may be adaptable to various modificationsand alternative forms, specific embodiments have been shown by way ofexample and described herein. However, it should be understood that thepresent disclosure is not intended to be limited to the particular formsdisclosed. Rather, it is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure asdefined by the appended claims. Moreover, the different aspects of thedisclosed apparatus and methods may be utilized in various combinationsand/or independently. Thus the invention is not limited to only thosecombinations shown herein, but rather may include other combinations.

What is claimed is:
 1. A device to manipulate at least one fluid packet,comprising: a reaction surface; and an array of electrodes operablycoupled to the reaction surface and adapted to generate electrical fielddistributions to impart manipulation forces on at least one fluid packetdisposed proximate the reaction surface, the array of electrodesincluding separate independently-addressable sets of electrodes to movethe at least one fluid packet about the reaction surface along at leastone selectively programmable path in at least two dimensions; where thereaction surface is an integrated circuit.
 2. The device of claim 1,wherein at least one of the sets of electrodes comprises a singleelectrode.
 3. The device of claim 1, wherein at least one of the sets ofelectrodes comprises a plurality of electrodes.
 4. The device of claim1, wherein the array of electrodes is further adapted to merge the atleast one fluid packet with at least one additional fluid packet.
 5. Thedevice of claim 1, wherein the array of electrodes is further adapted toperform at least one function selected from mixing or splitting the atleast one fluid packet.
 6. The device of claim 1, wherein each electrodeof the array of electrodes is individually addressable.
 7. The device ofclaim 1, further comprising a partitioning medium in which the at leastone fluid packet can be suspended.
 8. The device of claim 1, furthercomprising at least one of a dielectric coating or a hydrophobic coatingcovering the array of electrodes.
 9. The device of claim 1, whereinspacing of the electrodes of the array of electrodes is smaller than adiameter of the at least one fluid packet.
 10. A system to manipulate atleast one fluid packet, comprising: a device comprising: a reactionsurface, and an array of electrodes operably coupled to the reactionsurface and adapted to generate electrical field distributions to impartmanipulation forces on at least one fluid packet disposed proximate thereaction surface, the array of electrodes including separateindependently-addressable sets of electrodes; and a controller coupledto the array of electrodes and adapted to independently address at leastone of the sets of electrodes to generate electrical field distributionsto impart manipulation forces on the at least one fluid packet to movethe at least one fluid packet about the reaction surface along at leastone selectively programmable path in at least two dimensions; where thereaction surface is an integrated circuit.
 11. The system of claim 10,wherein at least one of the sets of electrodes comprises a singleelectrode.
 12. The system of claim 10, wherein at least one of the setsof electrodes comprises a plurality of electrodes.
 13. The system ofclaim 10, wherein the controller is further adapted to independentlyaddress the at least one of the sets of electrodes to merge the at leastone fluid packet with at least one additional fluid packet.
 14. Thesystem of claim 10, wherein the controller is further adapted toindependently address the at least one of the sets of electrodes toperform at least one function selected from mixing or splitting the atleast one fluid packet.
 15. The system of claim 10, wherein eachelectrode of the array of electrodes is individually addressable. 16.The system of claim 10, further comprising a partitioning medium inwhich the at least one fluid packet can be suspended.
 17. The system ofclaim 10, wherein the device further comprises at least one of adielectric coating or a hydrophobic coating covering the array ofelectrodes.
 18. The system of claim 10, wherein spacing of theelectrodes of the array of electrodes is smaller than a diameter of theat least one fluid packet.
 19. A method to manipulate at least one fluidpacket, comprising: providing a device comprising: a reaction surface,and an array of electrodes operably coupled to the reaction surface andadapted to generate electrical field distributions to impartmanipulation forces on at least one fluid packet disposed proximate thereaction surface, the array of electrodes including separateindependently-addressable sets of electrodes; where the reaction surfaceis an integrated circuit; disposing at least one fluid packet proximatethe reaction surface; and generating electrical field distributions byindependently addressing at least one of the sets of electrodes togenerate electrical field distributions to impart manipulation forces onthe at least one fluid packet to move the at least one fluid packetabout the reaction surface along at least one selectively programmablepath in at least two dimensions.
 20. The method of claim 19, wherein atleast one of the sets of electrodes comprises a single electrode. 21.The method of claim 19, wherein at least one of the sets of electrodescomprises a plurality of electrodes.
 22. The method of claim 19, furthercomprising merging the at least one fluid packet with at least oneadditional fluid packet.
 23. The method of claim 19, further comprisingperforming at least one function selected from mixing or splitting theat least one fluid packet.
 24. The method of claim 19, wherein eachelectrode of the array of electrodes is individually addressable. 25.The method of claim 19, further comprising a partitioning medium inwhich the at least one fluid packet can be suspended.
 26. The method ofclaim 19, wherein the device further comprises at least one of adielectric coating or a hydrophobic coating covering the array ofelectrodes.
 27. The method of claim 19, wherein spacing of theelectrodes of the array of electrodes is smaller than a diameter of theat least one fluid packet.